1. Field of the Invention
The present invention relates to a magnetic head, such as a thin-film magnetic head, which achieves improved bonding strength and stability of a ball bump for use in electrically connecting a connecting terminal of a head element and a conductive pattern for supplying an electric signal to the head element. The present invention also relates to a manufacturing method of the magnetic head, and to a bonding capillary used in the manufacturing method.
2. Description of the Related Art
FIG. 9 shows an overall configuration of a conventional thin-film magnetic head used in a hard magnetic disk device. The conventional thin-film magnetic head generally comprises a ceramic slider 1 having a head element formed of a thin film on its end face and serving to record on and reproduce information from a hard magnetic disk, a flexure 2 having flexibility and fixed at its leading end onto the underside of the slider 1 with an adhesive, an elastic load beam 3 made of stainless steel and fixed to the leading end of the flexure 2 by spot welding or the like, a mount 4 made of stainless steel and fixed to the rear and of the load beam 3 by spot welding or the like, a conductive pattern 8 mounted on the mount 4 so as to supply an electric signal to the head element, and a flexible wiring board 5 connected to the conductive pattern 8.
As shown in FIGS. 10 to 12 on an end face 1a of the slider 1 having a head element 6, four connecting terminals 7 (for recording and reproduction) made of gold-plated copper or nickel are arranged so as to establish an electrical connection with the head element 6. On the surface of the flexure 2, four conductive patterns 8, made of copper plated with gold via a polyimide resin layer, are formed, and the conductive patterns 8 are led out from the rear end of the flexure 2 to be electrically connected to the flexible wiring board 5.
The slider 1 is bonded to a tongue 2a formed at the leading end of the flexure 2. In this case, the end 1a of the slider 1 and the surface of the flexure 2 are orthogonal to each other, and the four connecting terminals 7 of the slider 1 are placed close to the ends of the corresponding four conductive patterns 8. Ball bumps 10 made of gold or the like are ultrasonically bonded to a corner portion 9 between the connecting terminals 7 and the conductive patterns 8 where the end face 1a of the slider 1 and the surface of the flexure 2 intersect, thereby electrically connecting terminals 7 and the conductive patterns 8.
A projection 3a formed at the leading end of the load beam 3 is in contact with the underside of the tongue 2a of the flexure 2, and presses the flexure 2 having elasticity against the underside of the slider 1 at a predetermined pressure.
In the magnetic head, although not shown, the mount 4 and the slider 1 are mounted opposed to a drive arm of the hard magnetic disk device and a magnetic recording surface of the magnetic disk, respectively. During operation, the slider 1 fixed to the flexure 2 floats above the magnetic recording surface of the magnetic disk at a predetermined distance while following the flow of air because of flexibility of the flexure 2, whereby magnetic recording on and reproduction from the magnetic disk are performed by the head element 6.
Next, a description will be given of a method of manufacturing the above-described magnetic head, in particular, a method of bonding the connecting terminal 7 and the conductive pattern 8 by the ball bump 10. FIG. 13 is a side view of a bonding capillary 11 made of a high-density ceramic, such as ruby or alumina (Al1O3), FIG. 14 is an enlarged view showing the principal part of a tip section of the capillary 11, and FIG. 15 is an end view of the tip section of the capillary 11. The capillary 11 consists of a cylindrical body section 11b having a through hole 11a in its center, and a tip section 11c that tapers off toward one end thereof. The tip section 11c has a recessed portion lid having a conical inner surface that communicates with an open end of the through hole 11a. 
As shown in FIG. 16, a fine wire 12 made of gold is passed through the through hole 11a in the capillary 11, and the leading end of the wire 12 projecting from the end face of the tip section 11c is melted by electric discharge, thereby forming a ball 12a. The ball 12a is held by the recessed portion lid formed in the tip section 11c. 
Next, the slider 1 fixed to the flexure 2 is held on a jig or the like (not shown) at an inclined angle of 45xc2x0, and the capillary 11 is lowered to face the corner portion 9 where the end face 1a of the slider 1 and the surface of the flexure 2 intersect, thereby bringing the ball 12a into contact with the surfaces of the connecting terminal 7 of the slider 1 and the conductive pattern 8 of the flexure 2. Then, the capillary 11 is ultrasonically vibrated in the direction parallel to the end face 1a of the slider 1 and the surface of the flexure 2 (orthogonal to the drawing sheet). Consequently, the ball 12a is simultaneously bonded to both the connecting terminal 7 and the conductive pattern 8, thereby forming a ball bump 10.
Finally, the wire 12 is pulled off the ball bump 10, and the electrical connection between the connecting terminal 7 and the conductive pattern 8 by the ball bump 10 is thereby completed. On the surface of the ball bump 10, a part of the severed wire 12, as shown in FIG. 17, remains as a residual portion 10a. 
In the above-described conventional bonding method using the ball 12a, the end of the tip section 11c of the capillary 11 in the lowered position is prone to be displaced from the corner portion 9, where the end face 1a of the slider 1 and the surface of the flexure 2 intersect, due to variations in positioning accuracy or other causes. For example, when the end of the tip section 11c is displaced toward the conductive pattern 8 by a distance t, the ball 12a held in the recessed portion 11d of the tip section 11c undergoes ultrasonic bonding in such a displaced state. Therefore, the ball bump 10 is bonded without contact with the connecting terminal 7 or without stable bonding strength.
Moreover, even when the ball 12a is precisely positioned at the corner portion 9, since the contact surfaces between the ball 12a, the connecting terminal 7 and the conductive pattern 8 are different in fractional force, the ball 12a rotates in the recessed portion 11d during bonding using ultrasonic vibration, which results in a prolonged bonding time, decreased bonding strength, etc.
The present invention has been made in view of the above-described problems. It is accordingly an object of the present invention to provide a magnetic head having a stable structure in which a connecting terminal and a conductive pattern are bonded by a ball bump with high bonding strength, a method of manufacturing the magnetic head, and a bonding capillary used in the method.
According to an aspect of the present invention, there is provided a magnetic head including a metal plate having a conductive pattern, and a slider fixed to the metal plate and having a head element and a connecting terminal electrically connected to the head element, wherein the connecting terminal and the conductive pattern are connected by ultrasonically bonding a metal ball thereto, and wherein a projecting portion is formed on the surface of the ball bump so as to extend in the direction that links the connecting terminal and the conductive pattern. In the above magnetic head, the projecting portion serves to prevent the ball bump from rotating during bonding, which allows a reliable magnetic head to be constructed in which a connecting terminal and a conductive pattern are bonded with high bonding strength.
According to another aspect of the present invention, there is provided a magnetic head manufacturing method including the steps of: fixing a slider having a head element and a connecting terminal electrically connected to the head element onto a metal plate having a conductive pattern; forming a groove in a tip section of a capillary having a through hole so as to cross the through hole, passing a wire through the through hole, and placing a ball formed at the end of the wire into the tip section; bringing the ball into contact with the connecting terminal and the conductive pattern by moving the tip section of the capillary; and forming a ball bump by ultrasonically vibrating the capillary in the direction orthogonal to the direction of the groove and bonding the ball to the connecting terminal and the conductive pattern. In this method, even when the tip section of the capillary is displaced, the ball held in the tip section is automatically placed by the groove at a predetermined position between the connecting terminal and the conductive pattern. Moreover, a part of the ball engages into the groove during welding, and the ball is thereby prevented from rotating, which permits firm bonding to be efficiently performed in a short time.
In the above-described magnetic head manufacturing method of the present invention, it is preferable that the value obtained by dividing the width of the groove by the diameter of the ball be greater than ⅙ and less than xc2xd. In this case, more reliable bonding can be achieved.
According to a further aspect of the present invention, there is provided a bonding capillary wherein a tip section having a through hole for passing a wire therethrough is provided with a recessed portion centered on the through hole, and a groove that reaches the outer surface of the tip section across the center of the recessed portion. This bonding capillary permits increases in bonding strength and reliability.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiment with reference to the attached drawings.